1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device with high characteristics. Note that a semiconductor device in the present specification generally indicates a device capable of functioning by utilizing semiconductor characteristics, and electro-optic devices, semiconductor circuits, and electronic devices are all semiconductor devices.
2. Description of the Related Art
In accordance with reduction in size of an integrated circuit, a semiconductor device which forms the integrated circuit is required to have lower contact resistance between a metal wiring and a semiconductor film and lower resistance of an impurity region in the semiconductor film. Therefore, a technique in which contact resistance and resistance of an impurity region are reduced by forming a silicide film on the semiconductor film has been adopted in a semiconductor field. When resistance of a semiconductor film is reduced, ON current of a semiconductor device is improved and a semiconductor device with high characteristics can be manufactured.
The silicide film is usually formed as follows: a CW (continuous-wave) laser or a pulsed laser with high repetition rate of 10 MHz or more (pseudo CW laser) is formed into a beam spot; an amorphous semiconductor film is irradiated with the laser; a solid-liquid interface to be formed by laser irradiation is moved to generate lateral crystal growth, so that a crystalline semiconductor film is formed; a metal film is formed thereover; and heat treatment is performed to react the crystalline semiconductor film and the metal film, whereby a silicide film is formed in the interface therebetween (for example, Reference 1: Japanese Published Patent Application No. H7-135324).
The crystalline semiconductor film obtained by the lateral crystal growth has characteristics that the crystals each have a large grain size and orientation of crystal planes in adjacent crystals with a large grain size is entirely different. The orientation of crystal planes in each crystal with a large grain size (hereinafter, referred to as large grain crystal) formed in a region irradiated with a laser beam is random; therefore, orientation of crystal planes in large grain crystals cannot be controlled in one direction.
Composition and a grow rate of the silicide to be formed is determined depending on the relation of surface energy between the semiconductor film and the silicide film to be formed. Accordingly, the silicide reaction between the metal film and the above crystalline semiconductor film in which the orientation of crystal planes in adjacent large grain crystals is random reflects random orientation of crystal planes in the semiconductor film. Thus, there is a problem in that composition and a thickness of silicide to be formed are not uniform.